In this study we will characterize the DNA of selected human herpesviruses and investigate the DNA base sequence homologies among those herpesviruses, including the Epstein-Barr virus, which is a candidate human tumor virus. The method is to construct a DNA heteroduplex composed, for example, of one DNA strand from herpes simplex virus type I and the complementary DNA strand from herpes simplex virus type 2. The heteroduplex is mounted for observation in the electron microscope, along with appropriate length standards. Regions of sufficient homology will appear duplex. Regions of insufficient homology will exist as two unpaired single strands. Detailed physical maps of base sequence homology will be achieved. BIBLIOGRAPHIC REFERENCE: The terminal repetition of Herpes Simplex Virus DNA. Graftstrom, R.H., J.C. Alwine, W.L. Steinhart, C.W. Hill, and Richard W. Hyman. Virology, in press, 1975.